Stress and strain inhomogeneities in cylindrical lithium-ion battery cells caused by formation and cyclic aging induced swelling have been investigated by a vast number of researchers and have been identified as a cause for inhomogeneous and significantly accelerated battery aging. Among those, one only recently described mechanism is Electrolyte motion induced salt inhomogeneity (EMSI), which can lead to drastically accelerated aging in tests with higher currents.

To investigate and describe this effect, our research group at BMW conducted various experimental and simulative studies. Among other approaches, one was to conduct computed tomography (CT) scans at different State of Charge (SOC) and State of Health (SOH) and to analyze them with a newly developed methodology, which is to be presented within this poster submission.

To apply this methodology, axial cross-sections are exported from VGL Studio. These are then consecutively imported with MATLAB and analyzed. For each cross-section, 360 grey-value profiles are evaluated at different angles from the cell can to the mandrel area. The distances from the cathode peaks in the grey-value profiles are used to determine the distances and thicknesses of the representative layer thicknesses consisting of anode (double layer coated), separator, cathode (double layer coated), separator. By repeating this process for all 360 angles and averaging across them, a precision can be achieved which exceeds the voxel size achieved by the raw CT-scan. This methodology generates an analysis of layer thicknesses across the entire battery, and also allows to compute the jelly roll diameters. This information can be used in further models for the calculation of electrode porosities and variations caused by swelling and aging.